Cellular differentiation of multicellular organisms is controlled by hormones and polypeptide growth factors. These diffusable molecules allow cells to communicate with each other and act in concert to form tissues and organs, and to repair and regenerate damaged tissue. Examples of hormones and growth factors include the steroid hormones, parathyroid hormone, follicle stimulating hormone, the interferons, the interleukins, platelet derived growth factor, epidermal growth factor, and granulocyte-macrophage colony stimulating factor, among others.
Hormones and growth factors influence cellular metabolism by binding to receptor proteins. Certain receptors are integral membrane proteins that bind with the hormone or growth factor outside the cell, and that are linked to signaling pathways within the cell, such as second messenger systems. Other classes of receptors are soluble intracellular molecules.
Cytokines generally stimulate proliferation or differentiation of cells of the hematopoietic lineage or participate in the immune and inflammatory response mechanisms of the body. Examples of cytokines which affect hematopoiesis are erythropoietin (EPO), which stimulates the development of red blood cells; thrombopoietin (TPO), which stimulates development of cells of the megakaryocyte lineage; and granulocyte-colony stimulating factor (G-CSF), which stimulates development of neutrophils. These cytokines are useful in restoring normal blood cell levels in patients suffering from anemia, thrombocytopenia, and neutropenia or receiving chemotherapy for cancer.
Cytokines play important roles in the regulation of hematopoiesis and immune responses, and can influence lymphocyte development. The human class II cytokine family includes interferon-α (IFN-α) subtypes, interferon-β (IFN-β), interferon-γ (IFN-γ), IL-10, IL-19 (U.S. Pat. No. 5,985,614), MDA-7 (Jiang et al., Oncogene 11, 2477-2486, (1995)), IL-20 (Jiang et al., Oncogene 11, 2477-2486, (1995)), IL-22 (Xie et al., J. Biol. Chem. 275, 31335-31339, (2000)), and AK-155 (Knappe et al., J. Virol. 74, 3881-3887, (2000)). Most cytokines bind and transduce signals through either Class I or Class II cytokine receptors. Members of human class II cytokine receptor family include interferon-αR1 (IFN-αR1), interferon-γ-R2 (IFN-γ-R2), interferon-γR1 (IFN-γR1), interferon-γR2 (IFN-γR2), IL-10R (Liu et al., J. Immunol. 152, 1821-1829, (1994)), CRF2-4 (Lutfalla et al. Genomics 16, 366-373, (1993)), IL-20Rβ (Blumberg et al., Cell 104, 9-19, (2001)) (also known as zcytor7 (U.S. Pat. No. 5,945,511) and CRF2-8 (Kotenko et al., Oncogene 19, 2557-2565, (2000)), IL-20Rβ (Blumberg et al., ibid, (2001)) (also known as DIRS1 (PCT WO 99/46379)), IL-22RA1 (IL-22 receptor-α1, submitted to HUGO for approval) (also known as IL-22R (Xie et al., J. Biol. Chem. 275, 31335-31339, (2000)), zcytor11 (U.S. Pat. No. 5,965,704) and CRF2-9 (Kotenko et al., Oncogene 19, 2557-2565, (2000)), and tissue factor.
Class II cytokine receptors are typically heterodimers composed of two distinct receptor chains, the α and β receptor subunits (Stahl et al., Cell 74, 587-590, (1993)). In general, the α subunits are the primary cytokine binding proteins, and the β subunits are required for formation of high affinity binding sites, as well as for signal transduction. An exception is the IL-20 receptor in which both subunits are required for IL-20 binding (Blumberg et al., ibid, (2001)).
The class II cytokine receptors are identified by a conserved cytokine-binding domain of about 200 amino acids (D200) in the extracellular portion of the receptor. This cytokine-binding domain is comprised of two fibronectin type III (FnIII) domains of approximately 100 amino acids each (Bazan J. F. Proc. Natl. Acad. Sci. USA 87, 6934-6938, (1990); Thoreau et al., FEBS Lett. 282, 16-31, (1991)). Each FnIII domain contains conserved Cys, Pro, and Trp residues that determine a characteristic folding pattern of seven β-strands similar to the constant domain of immunoglobulins (Uze et al., J. Interferon Cytokine Res. 15, 3-26, (1995)). The conserved structural elements of the class II cytokine receptor family make it possible to identify new members of this family on the basis of primary amino acid sequence homology. Previously we have successfully identified two new members of class II cytokine receptor family, zcytor7 (U.S. Pat. No. 5,945,511) (also known as IL-20R α (Blumberg et al., ibid, (2001)) and zcytor11 (U.S. Pat. No. 5,965,704) (also known as IL-22R (Blumberg et al., ibid, (2001)), using this approach. Identification of additional novel members of the class II cytokine receptor family is of interest because cytokines play a vital role in regulating biological responses.
IL-22, also known as IL-TIF (IL-10-related T cell-derived inducible factor) (Dumoutier et al., J. Immunology 164, 1814-1819, (2000)), is a recently described IL-10 homologue. Mouse IL-22 was originally identified as a gene induced by IL-9 in T cells and mast cells in vitro (Dumoutier et al., J. Immunology 164, 1814-1819, (2000)). Acute phase reactant induction activity was observed in mouse liver upon IL-22 injection, and IL-22 expression was rapidly induced after lipopolysaccharide (LPS) injection, suggesting that IL-22 contributes to the inflammatory response in vivo (Dumoutier et al., Proc. Natl. Acad. Sci. U.S.A. 97, 10144-10149, (2000)).
The interleukins are a family of cytokines that mediate immunological responses, including inflammation. The interleukins mediate a variety of inflammatory pathologies. Central to an immune response is the T cell, which produce many cytokines and adaptive immunity to antigens. Cytokines produced by the T cell have been classified as type 1 and type 2 (Kelso, A. Immun. Cell Biol. 76:300-317, 1998). Type 1 cytokines include IL-2, IFN-γ, LT-α, and are involved in inflammatory responses, viral immunity, intracellular parasite immunity and allograft rejection. Type 2 cytokines include IL-4, IL-5, IL-6, IL-10 and IL-13, and are involved in humoral responses, helminth immunity and allergic response. Shared cytokines between Type 1 and 2 include IL-3, GM-CSF and TNF-α. There is some evidence to suggest that Type 1 and Type 2 producing T cell populations preferentially migrate into different types of inflamed tissue.
Of particular interest, from a therapeutic standpoint, are the interferons (reviews on interferons are provided by De Maeyer and De Maeyer-Guignard, “Interferons,” in The Cytokine Handbook, 3rd Edition, Thompson (ed.), pages 491-516 (Academic Press Ltd. 1998), and by Walsh, Biopharmaceuticals: Biochemistry and Biotechnology, pages 158-188 (John Wiley & Sons 1998)). Interferons exhibit a variety of biological activities, and are useful for the treatment of certain autoimmune diseases, particular cancers, and the enhancement of the immune response against infectious agents, including viruses, bacteria, fungi, and protozoa. To date, six forms of interferon have been identified, which have been classified into two major groups. The so-called “type I” interferons include interferon-α, interferon-β, interferon-ω, interferon-δ, and interferon-τ. Currently, interferon-γ and one subclass of interferon-α are the only type II interferons.
Type I interferons, which are thought to be derived from the same ancestral gene, have retained sufficient similar structure to act by the same cell surface receptor. The α-chain of the human interferon-α/β receptor comprises an extracellular N-terminal domain, which has the characteristics of a class II cytokine receptor. Interferon-γ does not share significant homology with the type I interferons or with the type II interferon-α subtype, but shares a number of biological activities with the type I interferons.
In humans, at least 16 non-allelic genes code for different subtypes of interferon-α, while interferons β and ω are encoded by single genes. Type I interferon genes are clustered in the short arm of chromosome 9. Unlike typical structural human genes, interferon-α, interferon-β, and interferon-ω lack introns. A single gene for human interferon-γ is localized on chromosome 12 and contains three introns. To date, interferon-τ has been described only in cattle and sheep, while interferon-δ has been described only in pigs.
Clinicians are taking advantage of the multiple activities of interferons by using the proteins to treat a wide range of conditions. For example, one form of interferon-α has been approved for use in more than 50 countries for the treatment of medical conditions such as hairy cell leukemia, renal cell carcinoma, basal cell carcinoma, malignant melanoma, AIDS-related Kaposi's sarcoma, multiple myeloma, chronic myelogenous leukemia, non-Hodgkin's lymphoma, laryngeal papillomatosis, mycosis fungoides, condyloma acuminata, chronic hepatitis B, hepatitis C, chronic hepatitis D, and chronic non-A, non-B/C hepatitis. The U.S. Food and Drug Administration has approved the use of interferon-β to treat multiple sclerosis, a chronic disease of the nervous system. Interferon-γ is used to treat chronic granulomatous diseases, in which the interferon enhances the patient's immune response to destroy infectious bacterial, fungal, and protozoal pathogens. Clinical studies also indicate that interferon-γ may be useful in the treatment of AIDS, leishmaniasis, and lepromatous leprosy.
The demonstrated in vivo activities of the cytokine family illustrate the enormous clinical potential of, and need for, other cytokines, cytokine agonists, and cytokine antagonists. The present invention addresses these needs by providing a new cytokine that stimulates cells of the hematopoietic cell lineage, as well as related compositions and methods.